Systems and methods for controlling an aerial unit

ABSTRACT

An aerial unit that includes a first propeller; a second propeller that is spaced apart from the first propeller and is below the first propeller; a propelling module that is configured to rotate the first propeller and the second propeller about a first axis; an apertured duct that comprises a first duct portion and a second duct portion. The first duct portion surrounds the first propeller. The second duct portion surrounds the second propeller. The apertured duct defines at least one aperture at an intermediate area that is positioned below the first propeller and is above the second propeller. The aggregate size of the at least one aperture is at least fifty percent of a size of the intermediate area; a frame; and at least one steering element; an interfacing module arranged to be connected to a connecting element that couples the aerial unit to a ground unit. The propelling module and the duct are connected to the frame.

RELATED APPLICATIONS

This application is a continuation in part of U.S. nonprovisional patent application Ser. No. 13/814,244 filing date Feb. 5, 2013, which is a US national stage of PCT patent application PCT/IB2011/055021 International filing date Nov. 10, 2011 that claims priority from U.S. provisional patent 61/412,816 filing date Nov. 12, 2010, all incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

Prior art of height observation and signaling equipment (such as observation cameras) are connected to a base unit by using a mast made of rigid metal construction or other stiff materials that supports the equipment.

The mast implements large moments on the base due to its significant height. For example, every single Kg force of wind pressure at the top of a 30 meter height mast will implement a moment of about 30 Kg at one meter on the platform, and a pressure of about 150 Kg on a typical 20 cm diameter base construction. Thus, a heavy duty vehicle is required to support the equipment with its supporting construction.

In addition, the process of lifting the equipment to the destined altitude is time consuming and requires a team work. Tactic balloons and masts suffer from long spreading time, long folding time, large size (about 1 cubic meter of Helium for 300 gram of payload and balloon), bad stability and require highly trained operators.

There is a need for a simpler system and method for lifting equipment for height observation or signaling such as an observation camera.

SUMMARY

According to an embodiment of the invention an aerial unit is provided and includes a first propeller; a second propeller that is spaced apart from the first propeller and is below the first propeller; a propelling module that is configured to rotate the first propeller and the second propeller about a first axis; an apertured duct that comprises a first duct portion and a second duct portion; wherein the first duct portion surrounds the first propeller; wherein the second duct portion surrounds the second propeller; wherein the apertured duct defines at least one aperture at an intermediate area that is positioned below the first propeller and is above the second propeller; wherein an aggregate size of the at least one aperture is at least fifty percent of a size of the intermediate area; a frame that is connected to the propelling module and to the apertured duct; at least one steering element; and an interfacing module arranged to be connected to a connecting element that couples the aerial unit to a ground unit.

According to an embodiment of the invention a system may be provided and may include an aerial unit, a ground unit and a connecting element that connects the aerial unit to the ground unit. The ground unit may include a connecting element manipulator, for altering an effective length of the connecting element; wherein the effective length of the connecting element defines a distance between the ground unit and the aerial unit; a ground unit controller for controlling the connecting element manipulator; and a positioning unit arranged to image the aerial unit and to generate metadata about a location of the aerial unit; wherein the aerial unit comprises: a first propeller; a second propeller that is spaced apart from the first propeller and is below the first propeller; a propelling module that is configured to rotate the first propeller and the second propeller about a first axis; an apertured duct that comprises a first duct portion and a second duct portion; wherein the first duct portion surrounds the first propeller; wherein the second duct portion surrounds the second propeller; wherein the apertured duct defines at least one aperture at an intermediate area that is positioned below the first propeller and is above the second propeller; wherein an aggregate size of the at least one aperture is at least fifty percent of a size of the intermediate area; a frame that is connected to the propelling module and to the apertured duct; at least one steering element; and an interfacing module arranged to be connected to a connecting element that couples the aerial unit to a ground unit.

The height of the intermediate area may exceed a height of each one of the first and second duct portions.

The height of the intermediate area may exceed a sum of heights of the first and second duct portions.

The first and second duct portions may have an annular shape.

The first and second duct portions may or may not include any apertures.

The first and second duct portions may be spaced apart from each other and may be connected to each other by structural elements that are spaced apart from each other.

The aggregate size of the at least one aperture may be at least seventy five percent of a size of the intermediate area.

The aggregate size of the at least one aperture may be at least ninety percent of a size of the intermediate area.

The aggregate size of the at least one aperture may be at least ninety five percent of a size of the intermediate area.

The aerial unit further may include groups of additional propellers and additional propelling modules, each additional propelling module may be arranged to rotate a group of additional propellers; wherein each group of propellers may differ from the first and second propellers and may be positioned outside the duct.

A group of propellers of the groups of additional propellers may be surrounded by an additional apertured duct.

The additional apertured duct may define apertures that have an aggregate size that exceeds forty percent of a size of the additional apertured duct.

The group of propellers may include a first additional propeller and a second additional propeller and wherein the additional apertured duct may include a first additional duct portion and a second additional duct portion; wherein the first additional duct portion surrounds the first additional propeller; wherein the second additional duct portion surrounds the second additional propeller; wherein the additional apertured duct defines at least one additional aperture at an additional intermediate area that may be positioned below the first additional propeller and above the second additional propeller; wherein an aggregate size of the at least one additional aperture may be at least fifty percent of a size of the additional intermediate area.

Each group of propellers may be surrounded by an additional apertured duct.

Each group of propellers of the groups of additional propellers may be surrounded by an additional apertured duct.

Each additional apertured duct may define apertures that have an aggregate size that exceeds forty percent of a size of the additional apertured duct.

Each group of propellers may include a first additional propeller and a second additional propeller and wherein each additional apertured duct may include a first additional duct portion and a second additional duct portion; wherein the first additional duct portion surrounds the first additional propeller; wherein the second additional duct portion surrounds the second additional propeller; wherein the additional apertured duct defines at least one additional aperture at an additional intermediate area that may be positioned below the first additional propeller and above the second additional propeller; wherein an aggregate size of the at least one additional aperture may be at least fifty percent of a size of the additional intermediate area.

The additional propellers may be arranged in a symmetrical manner around the first propeller.

The additional propellers may be smaller than the first propeller.

The aerial unit may include a controller that may be arranged to independently control at least two propelling modules out of the propelling module and the additional propelling modules.

The controller may be arranged to independently control each propeller motor of the group of propeller motors.

The controller may be arranged to control one additional propeller motor to rotate in a clockwise manner and control another additional propeller motor to rotate in a counterclockwise manner.

The controller may be arranged to alter at least one of a location and an orientation of the aerial unit by controlling a thrust of at least two propellers of a group of propellers that may include the additional propeller and the first propeller.

The controller may be arranged to perform yaw steering by controlling the first propeller and at least one steering element that differs from the additional propellers; wherein the controller may be arranged to perform pitch and roll steering by controlling at least two additional propeller.

The controller may be arranged to perform yaw steering by controlling a thrust of first propeller and a thrust of at least one steering element that differs from the additional propellers; wherein the controller may be arranged to perform pitch and roll steering by controlling thrusts of at least two additional propellers.

The aerial unit may include a group of propellers that may include the first propeller, four additional propellers and a second propeller that rotates about a second axis that may be concentric to the first axis; wherein three propellers of the group of propellers rotate clockwise and three other propellers of the group rotate counter clockwise.

The aerial unit further may include a controller that may be arranged to control a change of at least one of a location and orientation of the aerial unit by altering at least one thrust of at least one propeller of the group while maintaining directions of rotation of the propellers of the group unchanged.

The positioning unit may be arranged to generate location metadata about a location of the aerial unit and wherein the aerial unit may include an orientation sensor arranged to generate orientation metadata about the orientation of the aerial unit.

The metadata may include location metadata and orientation metadata and wherein the controller may be arranged to control, at least in response to the metadata the at least one of the first propeller motor and the at least one steering element to affect at least one of the location of the aerial unit and the orientation of the aerial unit.

The frame at least partially surrounds the propeller; wherein the system may include additional propellers and additional propeller motors that are arranged to rotate the additional propellers; wherein each additional propeller may be positioned outside the frame; wherein the controller may be further arranged to control the additional propeller motors; and wherein the additional propeller motors are connected to additional frames; wherein the additional frames are coupled to the frame by coupling elements that allow movement between the frame and the additional frames.

According to an embodiment of the invention there may be provided an aerial unit that may include a first propeller; a second propeller that may be spaced apart from the first propeller and may be below the first propeller; a propelling module that may be configured to rotate the first propeller and the second propeller about a first axis; an apertured duct that may include a first duct portion and a second duct portion; wherein the first duct portion surrounds the first propeller; wherein the second duct portion surrounds the second propeller; wherein the first and second duct portions are spaced apart from each other and are connected to each other by structural elements that are spaced apart from each other.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will be apparent from the description below. The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:

FIG. 1 is a general view of a system according to an embodiment of the invention;

FIG. 2 is a general view of a system according to an embodiment of the invention;

FIG. 3 is a general view of an aerial unit of a system according to an embodiment of the invention;

FIG. 4 is a top view of an aerial unit of a system according to an embodiment of the invention;

FIGS. 5A-5D are cross sectional views of aerial units of systems according to embodiments of the invention;

FIG. 6 is a general view of an aerial unit of a system according to an embodiment of the invention;

FIG. 7 is a flow chart of a method according to an embodiment of the invention;

FIG. 8 illustrates an aerial unit according to an embodiment of the invention;

FIG. 9 is a top view of an aerial unit of a system according to an embodiment of the invention;

FIGS. 10A-10B are cross sectional views of aerial units according to various embodiment of the invention;

FIG. 11 is a cross sectional view of a prior art aerial unit and of air flows that flow through the aerial unit;

FIG. 12 is a cross sectional view of an aerial unit according to an embodiment of the invention and of air flows that flow through the aerial unit; and

FIGS. 13 and 14 are schematic diagrams illustrating apertured duct 320 according to various embodiments of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

A system is provided. The system may be used for height spreading of observation, signaling equipment, antennas, transmission relay station, anti-terrorist surveillance, and the like. The system may be a light, compact and portable and may include a ground unit and an aerial unit. The aerial unit orientation and location (displacement) may be controlled within four degrees of freedom while maintaining a built-in stability thereof. The system may be automatically and easily deployed and folded.

Various applications can use the system, for example: observation, height photographing, a reception/transmission relay, spot marking (by a projector or laser), antennas etc.

The system includes an aerial unit that may have an apertured duct. An apertured duct can (a) reduce the side forces applied by side winds, (b) reduce turbulences formed within the duct that reduce the efficiency of the aerial unit and introduce noise, (c) increase the effectiveness of lower propellers surrounded by the duct, (d) allow side air flows to contribute the overall thrust of the aerial unit and (e) provide higher thrusts.

FIG. 11 is a cross sectional view of a prior art aerial unit and of air flows that flow through the aerial unit while FIG. 12 is a cross sectional view of an aerial unit according to an embodiment of the invention and of air flows that flow through the aerial unit.

The side air flows 391 of FIG. 11 well exceed side air flows 391′ of FIG. 12—due to the smaller profile of the apertured duct of FIG. 12. The turbulences 393 of FIG. 11 do not develop in the apertured duct of FIG. 12. FIG. 12 also shows side air flows 394 that enters through apertures defined between first and second duct portions 3201 and 3202 and attribute to the thrust.

FIG. 1 illustrates a system 105 according to an embodiment of the invention having a ground unit 200 that is carried by a vehicle 222. FIG. 2 illustrates a system 107 according to an embodiment of the invention. It illustrates ground unit 200 as including an image processor 238 coupled to camera 232.

The system 105 includes, in addition to ground unit 200, an aerial unit 300 and a connecting element 400 that is arranged to connect the ground unit 200 to the aerial unit 300.

The ground unit 200 may include:

-   -   i. A connecting element manipulator 201, a base 202 and a ground         unit controller 203 (collectively denoted 210), the connecting         element manipulator 201 is arranged to alter an effective length         of the connecting element; wherein the effective length of the         connecting element defines a distance between the ground unit         and the aerial unit.     -   ii. A positioning unit 232 arranged to image the aerial unit and         to generate metadata about a location of the aerial unit.     -   iii. Controller 500 that may be arranged to apply various         control schemes and to determine the manner in which the aerial         unit 300 operates. The controller can control the speed and the         orientation of the aerial unit.

The aerial unit 200 may include a first propeller 310, second propeller 330, a propelling module that includes first and second propellers motors 312 and 332, a frame and at least one steering element (not shown). The first and second propellers are concentric.

Systems 105 and 107 are illustrated as including additional first and second propellers 340, 342, 344 and 346.

Aerial unit 300 of FIGS. 3,4 and 5A-5D is illustrates as including a pair of propellers as well as four additional propellers. These figures illustrate different folding arrangements of the four additional propellers.

FIGS. 5A-5D illustrate a rotation within an imaginary horizontal plane while FIG. 6 illustrates an aerial unit 302 that performs the folding within a vertical plane.

FIG. 5A is a top view of aerial unit 300 at an open configuration. FIG. 5B is a top view of aerial unit 302 at a closed configuration.

FIG. 5C is a side view of aerial unit 300 at a closed configuration where the additional propellers (for example 342 and 346) are located below the first and second propellers 310 and 330.

FIG. 5D is a side view of aerial unit 300 at a closed configuration where the additional propellers (for example 342 and 346) are located between the first and second propellers 310 and 330.

Any combination of components of each of the systems can be provided. The same applies to the aerial unit. For example, any one of systems 105 and 107 can be equipped with any of the aerial units 300, 302 and 304. Yet for another example, each system can include one or more video cameras, one or more orientation sensors and the like.

A system may be provided and may include a ground unit 200, an aerial unit 300 (of FIGS. 1-5 and 12) 302 (of FIGS. 6) and 304 (of FIGS. 8-10) and a connecting element 400 arranged to connect the ground unit 200 to the aerial unit 300, 302 and 304.

The ground unit 200 may include a connecting element manipulator 201, a base 202 and a ground unit controller 203 (collectively denoted 210).

The connecting element manipulator 201 is for altering an effective length of the connecting element 400. The effective length of the connecting element 400 defines a distance between the ground unit 200 and the aerial unit 300, 302 and 304.

The connecting element 400 can be a flexible cable that is maintained in a tensed status while the aerial unit 300 is in the air.

The aerial unit 300 can be arranged to maneuver in relation to the flexible cable, when the flexible cable is maintained in the tensed status.

The Flexible cable may include an electrical cable and a communication cable. These cables may be wrapped by or otherwise surrounded by flexible cable that provides a mechanical connectivity between the ground unit and the aerial unit.

The flexible cable is expected to physically tie and secure the aerial unit and electrically connect the ground unit and the aerial unit for power supply and communication. The aerial unit and the flexible cable do not require a special vehicle for support, as any van or relatively light vehicle can be adequate. Lighter versions of the system can even be carried by a person and even installed inside a backpack.

The flexible cable (once fully released) may be of 30 m length in order to get a good observation but other lengths may be used too. The average lifting and landing time of the aerial unit is around 10 seconds. The aerial unit may be configured to hold a payload of 1 to 5 kilos (although heavier or lighter payloads may be lifted by the aerial unit), may have a low heat emission and may barely generate noise. It is noted that flexible cables of other lengths may be used.

The base 202 is for receiving aerial unit and even for storing the aerial unit when the aerial unit is at its lowest position (ground position).

The ground unit controller 203 is for controlling the connecting element manipulator 201.

The ground unit 200 also includes a positioning unit 230 (see FIG. 2) that is arranged to image the aerial unit and to generate metadata about a location of the aerial unit. The position unit is illustrates in FIG. 1 as including video camera 232 and an image processor 238. It may include multiple video cameras. The metadata can refer to the location of the aerial unit, to the orientation of the aerial unit of both. It has been found that the image processing can be simplified by having the single video camera detect the location of the aerial unit while an orientation sensor can detect the orientation of the aerial unit.

According to various embodiment of the invention various aerial units 300 and 301 are provided. These aerial units may differ from each other by the number of propellers (second propeller 330, additional propellers 340, 342, 344 and 346, additional propellers 340′, 342′, 344′ and 246′), the manner in which payload is connected (to the aerial unit or to the connecting element 400), manner in which the additional propellers (if exist) converge when the aerial unit is in a close position, the number, shape and size of the additional propellers and the like, the type of electronic circuitry that is included in the aerial unit—from a controller to having only control wires and power lines the convey power and instructions to the various propeller motors.

Any of the aerial units 300, 302 and 304 may include (a) a first propeller 310, (b) a frame, (c) a first propeller motor 312 that is configured to rotate the first propeller 310 about a first axis, wherein the first propeller motor 312 is connected to the frame 333, (d) at least one steering element, and (e) an apertured duct 320. The at least one steering element can be a second propeller 330, one or more additional propellers 340, 342, 344 and 346 or any other steering element such as movable shelves.

At least one of the ground unit 200 and the aerial unit 300, 302 and 304 may include a controller (such as controller 500) that is arranged to control, at least in response to the metadata, at least one of the first propeller motor 312 and the at least one steering element to affect at least one of the location of the aerial unit 300, 302 and 304 and the orientation of the aerial unit 300, 302 and 304.

For simplicity of explanation controller 500 is illustrated as being a part of the ground unit 200 but this is not necessarily so.

As indicated above, the positioning unit may include a single video camera (232), multiple video cameras and at least two optical axes of at least two video cameras are oriented in relation to each other.

The video camera 232 can be proximate to point in which the connecting element 400 is connected to the ground unit—as shown, for example, in FIG. 1.

The video camera can be remotely positioned from the connecting element manipulator 201.

The image processor 238 may be arranged to determine a location of the aerial unit in relation to a desired location, and generate location metadata indicative of position corrections that should be made to position the aerial unit at the desired location. The location metadata can include positioning commands, the desired correction to be applied in order to return the aerial unit to a desired rotation and the like.

FIGS. and 1 and 2 also illustrates a connector 410 (such as a joint) that couples the flexible cable 400 to the aerial unit 300, while allowing the aerial unit 300 to move in relation to the flexible cable 400.

FIGS. 1 and 2 further illustrate a payload such as an interface electronic unit 420 that is positioned below the connector 410 and is arranged to send power and commands to the first motor. The interface electronic unit 420 can send commands to the various propeller motors in a format that is compliant to the formal acceptable by these various propeller motors. Placing the interface electronic unit 420 outside the aerial unit and without being supported by the aerial unit reduced the weight of the aerial unit and makes it easier to steer and manipulate.

FIGS. 1-3 illustrate a second propeller 330 that is arranged to rotate about a second axis; wherein the first and second axes are concentric. Yaw steering of the aerial unit can be facilitated by controlling the thrust of each of the first and second propellers 310 and 330, as illustrates by arrow 930 of FIG. 4.

The apertured frame 320 surrounds the first propeller 310 and surrounds the second propeller 330 but includes many apertures—as illustrated in further detail in FIG. 8.

According to an embodiment of the invention the system (see, for example, FIGS. 3 and 4) may include additional propellers 340, 342, 344 and 346, as well as additional propeller motors 350, 352, 354 and 356 that are arranged to rotate the additional propellers.

Each additional propeller is positioned outside the apertured duct 320. The controller 500 may be further arranged to control the additional propeller motors.

The additional propellers may be are arranged in a symmetrical manner around the first propeller 310.

The additional propellers 340, 342, 344 and 348 may be smaller than the first propeller 310.

The various propeller motors can be independently controlled by the controller 500.

The controller 500 can independently control at least two of the propeller motors. Thus, the thrust and the direction of such motors can differ from each other.

The controller 500 can be arranged to control one additional propeller motor to rotate in a clockwise manner and control another additional propeller motor to rotate in a counterclockwise manner. FIG. 4 illustrates three propellers that rotate clockwise (see arrow 902) and three other propeller that rotate counterclockwise (see arrow 901).

The controller 500 may alter at least one of a location and an orientation of the aerial unit 300 by controlling a thrust of at least two propellers of a group of propellers that includes the additional propeller and the first propeller.

The controller 500 may perform yaw steering by controlling the first propeller 310 and at least one steering element (such as second propeller 330) that differs from the additional propellers.

The controller 500 may perform pitch (910) and roll (920) steering by controlling at least two additional propellers.

The controller 500 may be arranged to control (by sending control signals) a change of at least one of a location and orientation of the aerial unit by altering at least one thrust of at least one propeller of the group while maintaining directions of rotation of the propellers of the group unchanged. An example is provided in FIG. 4—the direction of rotation remains unchanged. The following table illustrates a relationship between thrust differences and their meaning.

Difference between thrust of first and Yaw steering (rotation about second propellers 310 and 330 z-axis) Difference between thrust of first and Roll steering (rotation about third additional propellers 340 and 344 x-axis) Difference between thrust of second and Pitch steering (rotation about fourth additional propellers 342 and 346 y-axis)

For example, referring to the example set forth in FIG. 4, allowing the first propeller 310 to develop more thrust than the second propeller 330 will cause the aerial unit to rotate clockwise. Allowing the first additional propeller 340 to develop more thrust than the third additional propeller 330 will cause the aerial unit to rotate within an imaginary Y-Z plane, wherein the rotation starts by lowering the third additional propeller 330 while elevating the first additional propeller.

Various types of steering can be applied in order to set the aerial unit at a desired location, a desired orientation or both. If, for example, the wind causes the aerial unit to drift to a certain location the steering can be applied to counter that drift. FIG. 5 illustrates a field of view 600 of video camera 232, a current location 620 of the aerial unit, a desired location 610 of the aerial unit and a vector 630 that represents the desired location correction action.

Yet for another example, the steering can be applied in order to allow the aerial unit to fulfill a predefined flight pattern such as a scan pattern in which the aerial unit is directed along scan patters thus allowing its payload to change its field of view according to a desired pattern.

The additional propeller motors 350, 352, 354 and 356 and the additional propellers 340, 342, 344 and 346 may be positioned outside the apertured duct 320. The additional propeller motors 350, 352, 354 and 356 may be connected to additional frame elements 360, 362, 364 and 366. The additional ducts 321, 322, 324 and 326 can be are coupled to the apertured duct 320 by coupling elements 360, 362, 364 and 366 that allow movement between the aperture duct 320 and the additional frames.

This movement is required to facilitate the aerial unit to move between an open configuration to a close configuration. The coupling elements can be rods, arms, or any structural element that facilitates such movement.

When the additional frames are in an open condition the additional frames 321, 322, 324 and 326 and the frame 320 do not overlap and when the additional frames 321, 322, 324 and 326 are in a close condition the additional frames 321, 322, 324 and 326 and the frame 320 overlap.

The additional frames can change their position from a horizontal position to a vertical position—when moving from an open position to a closed position—as illustrated in FIG. 6, and especially by dashed arrows 940.

Additionally or alternatively, the movement from a closed position to an open position can take place in a horizontal plane—as illustrated by dashed arrows 930 of FIG. 5A.

The aerial unit can be in a closed position when proximate to the ground unit (at the beginning of the elevation process and at the end of the landing process). This can be done by activating motors that change the spatial relationship between the frame and the additional frames or by deactivating the additional propellers at the appropriate time.

Various figures such as FIGS. 1-2, illustrate the ground unit 200 as including a power source 240 and a user interface (not shown) that can allow a user to affect the control scheme—for example by determining the desired location. The user interface may include a joystick (or other man machine interface) for receiving positioning commands and, additionally or alternatively, for displaying the location of the aerial unit in relation to the desired location.

The power provided to the aerial unit can also be utilized for powering the payload 700.

The ground unit 200 may be positioned on a vehicle such as a van and aerial unit that holds a payload (such as one or more types of equipment) and can lift itself to heights of about thirty meters within approximately ten seconds. It is noted that the aerial unit can lift the equipment to heights that differ from thirty meters and during a period that differs than ten seconds.

The system does not require a physical support for the aerial unit that performs the observation from the heights, since the aerial unit supports itself. Thus—the flexible cable can be light weighted since it doesn't need to support aerial unit.

FIG. 7 illustrates method 1200 according to an embodiment of the invention.

Method 1200 may start by stage 1210 of tracking the location of an aerial unit by a positioning control unit that does not belong to the aerial unit.

Stage 1210 may be followed by stage 1220 of determining the relationship between the actual location of the aerial unit and a desired location.

Stage 1220 may be followed by stage 1230 of sending to the aerial unit positioning commands that affect the location of the aerial unit. The aerial unit may belong to a system as illustrated above. It may include, for example, a first propeller; a frame; a first propeller motor that is configured to rotate the first propeller about a first axis, wherein the first propeller motor is connected to the frame; an interfacing module for coupling a payload to the aerial unit; and additional propellers and additional propeller motors that are arranged to rotate the additional propellers; wherein each additional propeller is positioned outside the frame.

FIGS. 8 and 9 illustrate an aerial unit 304 according to an embodiment of the invention.

Aerial unit 304 includes a “main” group of propellers (first and second propellers 310 and 330) and four additional groups of propellers—first additional group of propellers includes first and second additional propellers 340 and 340′, second additional group of propellers includes first and second additional propellers 342 and 342′, third additional group of propellers includes first and second additional propellers 344 and 344′ and fourth additional group of propellers includes first and second additional propellers 346 and 346′.

The first till fourth additional groups of propellers are rotated by propelling modules 350′, 352′, 354′ and 356′. Each propelling module may include one or two propeller engines. Each additional propeller can have its own additional propeller motor.

The various propeller motors can be independently controlled by a controller such as controller 500 of FIG. 2. The controller 500 can independently control at least two of the propeller motors. Thus, the thrust and the direction of such motors can differ from each other.

FIGS. 8 and 9 illustrate that each one of the first till fourth groups of additional propellers are surrounded by apertured ducts 231′-234′. FIGS. 10A and 10B illustrate different folding manners of the additional ducts, propellers and propelling modules.

FIG. 8 illustrates the apertured duct 320 as including first and second duct portions 3201 and 3202 that are spaced apart from each other and are connected to each other via vertical structural elements 701. The vertical structural elements 701 are relatively small in relation to the intermediate area spanned between the first and second duct portions 3201 and 3202.

FIGS. 13 and 14 are schematic diagrams illustrating apertured duct 320 according to various embodiments of the invention.

In both FIGS. 13 and 14 two dashed curved lines 904 and 903 represent the space in which first propeller 310 rotates. The distance between curved dashed lines 904 and 903 represents the height of the first propeller 310.

In both FIGS. 13 and 14 two dashed curved lines 902 and 901 represent the space in which second propeller 310 rotates. The distance between curved dashed lines 902 and 901 represents the height of the second propeller 320.

An intermediate area spans between curved dashed line 903 (bottom of first propeller 310) and 902 (top of second propeller 330). The height of the intermediate area is represented by vertical arrows 910.

As can viewed by both FIGS. 13 and 14 most of the intermediate area is apertured—most of the space between the first and second propellers 310 and 330 is “empty”.

FIG. 13 illustrates the first duct portion 3201 as being spaced apart from the second duct portion 3202 and are connected by structural elements 701, the space between first and second duct portions 3201 and 302 and structural elements 701 form apertures 702.

FIG. 14 illustrates these portions (3201 and 3202) as being connected to each other to form a large aperture 702.

FIG. 13 also illustrates the upper and lower edges 32011 and 32012 of the first duct portion 3201 and the upper and lower edges 32021 and 32022 of the second duct portion 3202.

FIG. 13 illustrates the first duct portion 3201 as having an upper edge 32011 that is slightly above the upper edge (represented by dashed curved arrow 904) of first propeller 310 and has a lower edge 32012 that is slightly below the lower edge (represented by dashed curved arrow 903) of the first propeller 310. The height of the first duct portion 3201 can be about 1-10 (and preferably 2-6 times) times the height of the first propeller.

The second duct portion 3202 has an upper edge (32021) that is slightly above the upper edge (represented by dashed curved arrow 902) of second propeller 330 and has a lower edge (32022) that is slightly below the lower edge (represented by dashed curved arrow 901) of the second propeller 330. The height of the second duct portion can be about 1-10 (and preferably 2-6 times) times the height of the second propeller.

The first and second duct portions can be connected to each other—but in any case the apertured duct should include apertures of substantial size in relation to the overall size of the apertured duct.

The first duct portion 3201 has an annular shape and it surrounds first propeller 310. The upper and lower edges of the

Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art, accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. 

1. An aerial unit, comprising: a first propeller; a second propeller that is spaced apart from the first propeller and is below the first propeller; a propelling module that is configured to rotate the first propeller and the second propeller about a first axis; an apertured duct that comprises a first duct portion and a second duct portion; wherein the first duct portion surrounds the first propeller; wherein the second duct portion surrounds the second propeller; wherein the apertured duct defines at least one aperture at an intermediate area that is positioned below the first propeller and is above the second propeller; wherein an aggregate size of the at least one aperture is at least fifty percent of a size of the intermediate area; a frame that is connected to the propelling module and to the apertured duct; at least one steering element; and an interfacing module arranged to be connected to a connecting element that couples the aerial unit to a ground unit.
 2. The aerial unit according to claim 1, wherein a height of the intermediate area exceeds a height of each one of the first and second duct portions.
 3. The aerial unit according to claim 1, wherein a height of the intermediate area exceeds a sum of heights of the first and second duct portions.
 4. The aerial unit according to claim 1, wherein the first and second duct portions have an annular shape.
 5. The aerial unit according to claim 1, wherein the first and second duct portions do not include any apertures.
 6. The aerial unit according to claim 1, wherein the first and second duct portions are spaced apart from each other and are connected to each other by structural elements that are spaced apart from each other.
 7. The aerial unit according to claim 1, wherein the aggregate size of the at least one aperture is at least seventy five percent of a size of the intermediate area.
 8. The aerial unit according to claim 1, wherein the aggregate size of the at least one aperture is at least ninety percent of a size of the intermediate area.
 9. The aerial unit according to claim 1, wherein the aggregate size of the at least one aperture is at least ninety five percent of a size of the intermediate area.
 10. The aerial unit according to claim 1, further comprising groups of additional propellers and additional propelling modules, each additional propelling module is arranged to rotate a group of additional propellers; wherein each group of propellers differs from the first and second propellers and is positioned outside the duct.
 11. The aerial unit according to claim 10, wherein a group of propellers of the groups of additional propellers is surrounded by an additional apertured duct.
 12. The aerial unit according to claim 11, wherein the additional apertured duct defines apertures that have an aggregate size that exceeds forty percent of a size of the additional apertured duct.
 13. The aerial unit according to claim 11, wherein the group of propellers comprises a first additional propeller and a second additional propeller and wherein the additional apertured duct comprises a first additional duct portion and a second additional duct portion; wherein the first additional duct portion surrounds the first additional propeller; wherein the second additional duct portion surrounds the second additional propeller; wherein the additional apertured duct defines at least one additional aperture at an additional intermediate area that is positioned below the first additional propeller and above the second additional propeller; wherein an aggregate size of the at least one additional aperture is at least fifty percent of a size of the additional intermediate area.
 14. The aerial unit according to claim 10, wherein each group of propellers is surrounded by an additional apertured duct.
 15. The aerial unit according to claim 14, wherein each group of propellers of the groups of additional propellers is surrounded by an additional apertured duct.
 16. The aerial unit according to claim 15, wherein each additional apertured duct defines apertures that have an aggregate size that exceeds forty percent of a size of the additional apertured duct.
 17. The aerial unit according to claim 15, wherein each group of propellers comprises a first additional propeller and a second additional propeller and wherein each additional apertured duct comprises a first additional duct portion and a second additional duct portion; wherein the first additional duct portion surrounds the first additional propeller; wherein the second additional duct portion surrounds the second additional propeller; wherein the additional apertured duct defines at least one additional aperture at an additional intermediate area that is positioned below the first additional propeller and above the second additional propeller; wherein an aggregate size of the at least one additional aperture is at least fifty percent of a size of the additional intermediate area.
 18. The aerial unit according to claim 14, wherein the additional propellers are arranged in a symmetrical manner around the first propeller. 19-20. (canceled)
 21. A system, comprising an aerial unit, a ground unit and a connecting element that connects the aerial unit to the ground unit; wherein the ground unit comprises: a connecting element manipulator, for altering an effective length of the connecting element; wherein the effective length of the connecting element defines a distance between the ground unit and the aerial unit; a ground unit controller for controlling the connecting element manipulator; and a positioning unit arranged to image the aerial unit and to generate metadata about a location of the aerial unit; wherein the aerial unit comprises: a first propeller; a second propeller that is spaced apart from the first propeller and is below the first propeller; a propelling module that is configured to rotate the first propeller and the second propeller about a first axis; an apertured duct that comprises a first duct portion and a second duct portion; wherein the first duct portion surrounds the first propeller; wherein the second duct portion surrounds the second propeller; wherein the apertured duct defines at least one aperture at an intermediate area that is positioned below the first propeller and is above the second propeller; wherein an aggregate size of the at least one aperture is at least fifty percent of a size of the intermediate area; a frame that is connected to the propelling module and to the apertured duct; at least one steering element; and an interfacing module arranged to be connected to a connecting element that couples the aerial unit to a ground unit. 22-40. (canceled)
 41. An aerial unit, comprising: a first propeller; a second propeller that is spaced apart from the first propeller and is below the first propeller; a propelling module that is configured to rotate the first propeller and the second propeller about a first axis; an apertured duct that comprises a first duct portion and a second duct portion; wherein the first duct portion surrounds the first propeller; wherein the second duct portion surrounds the second propeller; wherein the first and second duct portions are spaced apart from each other and are connected to each other by structural elements that are spaced apart from each other. 